The invention relates to dynamoelectric machine cooling systems and in particular, to dynamoelectric machines wherein coolant flows from a passage in the machine housing to an internal passageway in the shaft of the machine rotor.
In a number of prior art machines, a coolant transfer tube is provided to allow the coolant to flow under pressure from the machine housing to an internal passage in the rotor shaft. Normally, the transfer tube is secured to either the housing of the machine or to the rotor shaft. This arrangement generally requires a number of parts in addition to the tube, including a pin or other device for preventing the transfer tube from rotating with respect to the housing or shaft and an O-ring or some other sealing arrangement to prevent the coolant from escaping from the transfer tube into the machine. One of the principal disadvantages of this type of structure for high generators that are used, for example, in aircraft, is that the end of the transfer tube that is not secured will be rotating against a bearing surface at the same speed as the generator is rotating. In aircraft-type generators this can be on the order 12,000 rpm, which could result in significant wear of the bearing surfaces. In addition, securing one end of the tube to either the housing or the shaft results in a somewhat rigid structure which only permits very limited articulation or flexing of the tube as the generator's shaft flexes under load, thereby contributing to even more wear of the bearing surfaces. Thus, the securing of one end of the transfer tube to either the housing or the shaft results in increased bearing wear and the necessity for using fastening means with the attendant manufacturing and assembly cost of those parts.